Re: [PATCH 1/7] icmp, udp: Pad time_t timestamp to 64-bit to ease state migration

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Jan 28, 2025 at 12:15:26AM +0100, Stefano Brivio wrote:
> That's the only field in flows with different storage sizes depending
> on the architecture: it's usually 4-byte wide on 32-bit architectures,
> except for arc and x32 where it's 8 bytes, and 8-byte wide on 64-bit
> machines.

As discussed on the call, I think there are broader problems with
transferring timestamps than just the structure size.  So I'm hoping
we can work out how to not transfer them at all and avoid this change.

> By keeping flow entries the same size across architectures, we avoid
> having to expand or shrink table entries upon migration.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> ---
>  icmp_flow.h | 6 +++++-
>  udp_flow.h  | 6 +++++-
>  2 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/icmp_flow.h b/icmp_flow.h
> index fb93801..da7e255 100644
> --- a/icmp_flow.h
> +++ b/icmp_flow.h
> @@ -13,6 +13,7 @@
>   * @seq:	Last sequence number sent to tap, host order, -1: not sent yet
>   * @sock:	"ping" socket
>   * @ts:		Last associated activity from tap, seconds
> + * @ts_storage:	Pad @ts to 64-bit storage to keep state migration sane
>   */
>  struct icmp_ping_flow {
>  	/* Must be first element */
> @@ -20,7 +21,10 @@ struct icmp_ping_flow {
>  
>  	int seq;
>  	int sock;
> -	time_t ts;
> +	union {
> +		time_t ts;
> +		uint64_t ts_storage;
> +	};
>  };
>  
>  bool icmp_ping_timer(const struct ctx *c, const struct icmp_ping_flow *pingf,
> diff --git a/udp_flow.h b/udp_flow.h
> index 9a1b059..9cb79a0 100644
> --- a/udp_flow.h
> +++ b/udp_flow.h
> @@ -12,6 +12,7 @@
>   * @f:		Generic flow information
>   * @closed:	Flow is already closed
>   * @ts:		Activity timestamp
> + * @ts_storage:	Pad @ts to 64-bit storage to keep state migration sane
>   * @s:		Socket fd (or -1) for each side of the flow
>   */
>  struct udp_flow {
> @@ -19,7 +20,10 @@ struct udp_flow {
>  	struct flow_common f;
>  
>  	bool closed :1;
> -	time_t ts;
> +	union {
> +		time_t ts;
> +		uint64_t ts_storage;
> +	};
>  	int s[SIDES];
>  };
>  

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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